Re: Potential ABI breakage in upcoming minor releases

Hi Macro,

> I looked a bit at this out of interest. I see an assert failure in the
> lines below when running tests with TimescaleDB compiled against 17.0
> with 17.1 installed. Without the assertion it would anyway segfault
> below.
>
> /*
> * Usually, mt_lastResultIndex matches the target rel. If it happens not
> * to, we can get the index the hard way with an integer division.
> */
> whichrel = mtstate->mt_lastResultIndex;
> if (resultRelInfo != mtstate->resultRelInfo + whichrel)
> {
> whichrel = resultRelInfo - mtstate->resultRelInfo;
> Assert(whichrel >= 0 && whichrel < mtstate->mt_nrels);
> }
>
> updateColnos = (List *) list_nth(node->updateColnosLists, whichrel);
>
> The problem here is that because TimescaleDB compiled against 17.0
> assumes a struct size of 376 (on my laptop) while PostgreSQL allocated
> the array with a struct size of 384, so the pointer math no longer
> holds and the whichrel value becomes nonsense. (1736263376 for
> whatever reason)

Thanks for reporting. Yes, the code assumed fixed
sizeof(ResultRelInfo) within a given PG major release branch which
turned out not to be the case. We will investigate whether it can be
easily fixed on TimescaleDB side.

--
Best regards,
Aleksander Alekseev